Key Takeaways
- The heart has four chambers with the left ventricle being the strongest; blood flows: vena cava → RA → RV → pulmonary arteries → lungs → pulmonary veins → LA → LV → aorta
- Cardiac output (CO) = Stroke Volume (SV) x Heart Rate (HR); normal CO is approximately 5 L/min at rest
- Blood pressure is determined by: BP = CO x Total Peripheral Resistance (TPR); normal resting BP is <120/80 mmHg
- The cardiac conduction system pathway: SA node (60-100 bpm) → AV node (40-60 bpm) → Bundle of His → bundle branches → Purkinje fibers (20-40 bpm)
- Pulmonary ventilation involves the mechanics of breathing: inspiration is active (diaphragm contracts), expiration is passive at rest (elastic recoil)
- Gas exchange occurs at the alveolar-capillary membrane via diffusion; factors affecting diffusion include surface area, membrane thickness, and pressure gradient
- Oxygen is carried primarily bound to hemoglobin (98.5%) and dissolved in plasma (1.5%); the oxyhemoglobin dissociation curve shifts right with increased temperature, CO2, and acidity
- Normal arterial blood gas values: pH 7.35-7.45, PaO2 80-100 mmHg, PaCO2 35-45 mmHg, HCO3 22-26 mEq/L, SaO2 95-100%
Cardiopulmonary Anatomy & Physiology
The cardiovascular and pulmonary systems work together to deliver oxygen to tissues and remove carbon dioxide. Physical therapists must understand these systems to safely prescribe exercise and manage patients with cardiopulmonary conditions.
Cardiac Anatomy and Physiology
Heart Chambers, Valves, and Blood Flow
| Structure | Function |
|---|---|
| Right Atrium | Receives deoxygenated blood from SVC and IVC |
| Tricuspid Valve | Prevents backflow from RV to RA |
| Right Ventricle | Pumps blood to pulmonary arteries |
| Pulmonary Valve | Prevents backflow from pulmonary artery to RV |
| Left Atrium | Receives oxygenated blood from pulmonary veins |
| Mitral (Bicuspid) Valve | Prevents backflow from LV to LA |
| Left Ventricle | Pumps blood to aorta and systemic circulation |
| Aortic Valve | Prevents backflow from aorta to LV |
Cardiac Cycle
The cardiac cycle consists of systole (contraction) and diastole (relaxation):
- Isovolumetric contraction: All valves closed, pressure builds in ventricles
- Ventricular ejection: Semilunar valves open, blood ejected into aorta/pulmonary artery
- Isovolumetric relaxation: All valves closed, pressure drops in ventricles
- Ventricular filling: AV valves open, blood fills ventricles passively and with atrial contraction (atrial kick)
Cardiac Output and Hemodynamics
Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR)
- Normal resting CO: ~5 L/min
- During maximal exercise: CO can increase to 20-25 L/min in healthy adults
Blood Pressure = Cardiac Output x Total Peripheral Resistance
- Systolic BP: Pressure during ventricular contraction (normal <120 mmHg)
- Diastolic BP: Pressure during ventricular relaxation (normal <80 mmHg)
- Mean Arterial Pressure (MAP) = DBP + 1/3(SBP - DBP); normal ~93 mmHg; MAP <60 mmHg indicates inadequate organ perfusion
Coronary Arteries
| Artery | Area Supplied |
|---|---|
| Left Anterior Descending (LAD) | Anterior wall LV, anterior 2/3 interventricular septum |
| Left Circumflex (LCx) | Lateral and posterior walls of LV |
| Right Coronary Artery (RCA) | RV, inferior wall LV, SA node (60%), AV node (85%) |
Critical Point: Coronary perfusion occurs primarily during diastole. An increased heart rate shortens diastole, reducing coronary blood flow — this is why tachycardia can trigger angina in patients with coronary artery disease.
Pulmonary Anatomy and Physiology
Mechanics of Breathing
| Phase | Muscles | Process |
|---|---|---|
| Quiet inspiration | Diaphragm (primary), external intercostals | Active — diaphragm contracts and descends, thorax expands, negative intrapulmonary pressure draws air in |
| Forced inspiration | Accessory muscles (SCM, scalenes, pectoralis minor) | Active — additional muscles increase thoracic expansion |
| Quiet expiration | None (passive) | Elastic recoil of lungs and chest wall |
| Forced expiration | Internal intercostals, abdominals | Active — muscles compress thorax to force air out |
Lung Volumes and Capacities
| Volume/Capacity | Description | Normal Adult Value |
|---|---|---|
| Tidal Volume (TV) | Air moved in one normal breath | ~500 mL |
| Inspiratory Reserve (IRV) | Additional air inhaled after normal inspiration | ~3,100 mL |
| Expiratory Reserve (ERV) | Additional air exhaled after normal expiration | ~1,200 mL |
| Residual Volume (RV) | Air remaining after maximal expiration | ~1,200 mL |
| Vital Capacity (VC) | TV + IRV + ERV | ~4,800 mL |
| Total Lung Capacity (TLC) | VC + RV | ~6,000 mL |
| Functional Residual Capacity (FRC) | ERV + RV | ~2,400 mL |
Arterial Blood Gas (ABG) Interpretation
| Parameter | Normal Value | Interpretation |
|---|---|---|
| pH | 7.35-7.45 | <7.35 = acidosis; >7.45 = alkalosis |
| PaO2 | 80-100 mmHg | <80 = hypoxemia |
| PaCO2 | 35-45 mmHg | >45 = respiratory acidosis; <35 = respiratory alkalosis |
| HCO3 | 22-26 mEq/L | <22 = metabolic acidosis; >26 = metabolic alkalosis |
| SaO2 | 95-100% | Hemoglobin oxygen saturation |
ABG Interpretation Steps:
- Check pH: acidosis (<7.35) or alkalosis (>7.45)?
- Check PaCO2: respiratory component
- Check HCO3: metabolic component
- Determine primary cause and whether compensation is present
Coronary perfusion occurs primarily during which phase of the cardiac cycle?
A patient has the following ABG results: pH 7.30, PaCO2 55 mmHg, HCO3 24 mEq/L. This indicates:
A patient with a stroke volume of 65 mL and heart rate of 80 bpm has a cardiac output of:
Normal tidal volume in an adult is approximately _____ mL.
Type your answer below
During quiet breathing, expiration is:
The LAD (left anterior descending) coronary artery primarily supplies blood to which area of the heart?
A patient ABG results show: pH 7.50, PaCO2 28 mmHg, HCO3 24 mEq/L. This indicates:
Mean arterial pressure (MAP) below which value indicates inadequate organ perfusion?